Taking place between Seasons 4 and 5, the ninjas, having defeated Chen, are attacked by a new threat by the name of Ronin. When the ninjas try to stop Ronin, he uses a new weapon, the Obsidian Glaive, to steal the ninjas' memories and powers, reverting them to the way they were when they first met. Sensei Wu tells the ninjas that the only way they can regain their memories and powers is to obtain Obsidian Weapons of their own, so the ninjas go on a quest to obtain the Obsidian Weapons and put a stop to Ronin's plans.
LEGO Ninjago: Shadow of Ronin contains examples of:
- Actually Pretty Funny: Sensei Wu can be seen and heard laughing when Jay tries to cover up that he wanted to bring his laundry to his parents in front of Nya.
- Adaptational Weapon Swap: Zane's signature weapon is changed from shurikens to sai in this game. This also applies to his Obsidian Weapon, which are based off the original Golden Weapons.
- Big "NO!": Jay has one when Kai gets a call from Nya about Nindroids attacking Ninjago, which delays the quest to obtain his Obsidian Nunchucks.
- Bookends: The game opens and closes with Kai telling a story that ends with Jay losing his pants.
- Brick Joke: In Kai's retelling of the ninjas' time on Chen's island, the story ends with Jay losing his pants, which makes him tell Kai that's not how the story went. At the end of the game, Jay once again loses his pants and he once again stops Kai's story by telling him that's not what happened.
- Call-Back: Lloyd is still recovering from his father's Heroic Sacrifice from the Season 4 finale "The Corridor of Elders".
- Destroy the Villain's Weapon:
- In the Fulcrum Chamber, when it's revealed Ronin brainwashed Misako to betray the ninjas, Lloyd uses his elemental beam to break his Obsidian Glaive.
- When the Elemental Forges are weakened from Ronin using them, the ninjas foil Ronin's plan by depleting the last of their energy and destroying the Primal Fulcrum to make the portal collapse.
- Dissimile: In the Fire Temple, when Kai's memories come back to him:Kai: This is so weird. This is like a cheese-dream. Only I'm awake. And I didn't eat any cheese.
- False Reassurance: When Cole gets nervous about using the jetpacks Jay built to escape the volcano of the Fire Temple:Kai: Look at it this way, Cole; You're choosing between almost certainly being barbecued-
Cole: Or using the jetpacks, I get it.
Kai: No, no, that first option was the jetpacks. These things look really dangerous.
- Fun with Homophones:
Cole: Uh, what has two eyes and is really scary?
- In Kai's retelling of the ninjas' time on Chen's island, when Cole tries to warn Kai of the Anacondrai serpent behind him:
Kai: Uh..."evil spirits"? Oh no, wait, that has three I's...
- When the ninjas drink the Tea of Insight, they learn where their Obsidian Weapons are. When Zane sees his, there's this exchange:
Jay: Sorry, Zane, are we boring you?
Zane: Obsidian Sais! I can see a pair of them!
- Funny Background Event: After Kai's jetpack breaks down while escaping the Fire Temple, Jay apologizes and says that he was expecting Cole's jetpack to be the one that breaks down. After Cole expresses his disapproval, his jetpack in the background explodes.
- Her Codename Was Mary Sue: In Kai's retelling of the ninjas' time on Chen's island, Kai finds opportunities for him to come up with good ideas and have the other ninjas compliment him.
- Hydro-Electro Combo: After Ronin acquires the Elemental Forge of Earth, Dareth tries to stop Ronin by using the combined energies of the Elemental Forges he has. Unfortunately, the Elemental Forges he uses are of Ice and Fire, which create a pool of water around him. Ronin uses the Elemental Forge of Lightning to electrify the water around Dareth, allowing him to take Dareth's Elemental Forges.
- Laser-Guided Amnesia: Ronin's Obsidian Glaive robs the ninjas of their memories and resets them to the way they were back when they first met. The ninjas are later told that it could've done much worse than steal their memories; they could've been brainwashed by Ronin.
- Leaning on the Fourth Wall: When Zane is fighting the Ice Serpent:Jay: Yeah! Show it who's boss. Although if this was a video game, it'd still be the giant snake.
- Lost Food Grievance: In Chen's Palace, one of Ronin's guards won't open a door the ninjas need to get through until he receives his food order, so the ninjas have to make it for him. Give him the wrong order and he'll put it in the trash, which upsets Cole because he wanted to eat it. A Gold Brick is earned for doing this.
- The Stinger: After the ending of the game, a mysterious character puts on the Helmet of Shadows that controls the Stone Warriors...who turns out to be Dareth making them do his chores for him.
- Stock Scream: At Ed and Edna's Scrap 'n Junk, one of the Fangpyres gives a Wilhelm scream when a bunch of tires fall on him.
- That Came Out Wrong: At Ed and Edna's Scrap 'n Junk, when Jay says he forgot to bring his laundry over, Jay tries to cover it up by saying it's his mother's laundry, but he realizes that sounds worse and clarifies it's his own laundry.